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The results of the neutrino experiment shook the world of physics

The head of an experiment that appeared to show subatomic particles travelling faster than the speed of light has resigned from his post.

Prof Antonio Ereditato oversaw results that appeared to challenge Einstein's theory that nothing could travel faster than the speed of light.

Reports said some members of his group, called Opera, had wanted him to resign.

Earlier in March, a repeat experiment found that the particles, known as neutrinos, did not exceed light speed.

When the results from the Opera group at the Gran Sasso underground laboratory in Italy were first published last year, they shocked the world, threatening to upend a century of physics as well as relativity theory - which holds the speed of light to be the Universe's absolute speed limit.

The experiment involved measuring the time it took for neutrinos to travel the 730km (450 miles) from Cern laboratory in Geneva, Switzerland to the lab in Italy.

Call for caution

Speaking at the time, Professor Ereditato added "words of caution" because of the "potentially great impact on physics" of the result.

"We tried to find all possible explanations for this," he said.

"We wanted to find a mistake - trivial mistakes, more complicated mistakes, or nasty effects - and we didn't.

"When you don't find anything, then you say 'well, now I'm forced to go out and ask the community to scrutinise this'."

Despite the call for caution, the results caused controversy within the world of physics.

If the findings had been confirmed, they would have disproved Albert Einstein's 1905 Special Theory of Relativity.

Earlier this month, a test run by a different group at the same Italian laboratory recorded neutrinos travelling at precisely light speed.

Sandro Centro, co-spokesman for the Icarus collaboration, said that he was not surprised by the result.

"In fact I was a little sceptical since the beginning," he told BBC News at the time.

"Now we are 100% sure that the speed of light is the speed of neutrinos."

So far, Professor Ereditato has not commented on his decision to step down from his post.